This invention relates to minimally invasive cryosurgery. More particularly, this invention concerns the structure and the method of operation of a cryosurgical apparatus, which consists of one or more cryoprobes and a pressurized cryofluid source.
Cryosurgery, or the destruction of undesired biological tissues by freezing, has long been accepted as an important alternative technique of surgery (Orpwood, 1981; Rubinsky and Onik, 1991; Gage, 1992). Compared with conventional means of destroying tissues, such as surgical excision, radiotherapy and chemotherapy, visceral cryosurgery (especially minimal-invasive cryosurgery) offers the following potential advantages: simplicity of the procedure, minimal bleeding, anaesthetic effect of low temperatures, short period of patient recovery, low cost, minimal scarring, and possible stimulation of the body's immune system.
James Arnott, an English physician, was the first to introduce the technique of destruction of biological tissues by freezing in 1865. Since Arnott's first report, numerous cryodevices and techniques have been suggested. These have included pre-cooled metal blocks, spray/pour freezing with compressed or liquefied applications, cryogenic heat pipes, Joule-Thompson effect based cryoprobes and boiling effect based cryoprobes. However, as a result of the high cooling power usually needed for cryosurgery, and especially of internal organs, the boiling effect and the Joule-Thompson effect have been found to be the preferable cooling technique by most cryosurgeons.
Minimally invasive cryosurgery is monitored by ultrasound, CT or MRI; however, ultrasound is the most accepted imaging technique among cryosurgeons today. Utilizing these techniques, the cryosurgeon inserts the cryoprobe(s) into the region to be cryotreated. Then, the cryosurgeon activates the cryoprobe(s) according to a cooling protocol and monitors the frozen region growth (which is also termed "ice-ball"). When the undesired tissues are completely frozen, or when there is a danger of cryodestruction to important surrounding tissues, the cryosurgeon terminates the cooling process and the thawing stage follows. In some cases the cooling.backslash.thawing stages are repeated in order to increase cryodestruction.
The application of minimal-invasive cryosurgery calls for: a cryoprobe insertion technique that causes minimal damage to the surrounding healthy tissues, an accurate localization of the cryoprobe tip, and a precise monitoring of the frozen region formation. These criteria have served as the motivation for the continued efforts toward the reduction of cryoprobe diameter and improvement in imaging techniques. Ultimately, the cryoprobe diameter is a result of the diameter of the cryofluid tubes and by the cryoprobe's thermal insulator thickness. Since a typical cryoprobe diameter is relatively large, a pathway must be provide for the cryoprobe into the cryotreated region. An alternative solution for this problem is given by the invention presented hereby.